Method of producing alloys of lead and alkali metals



Un ted S ews 2, 0,2 6 'ME-THOD F PROD. ING' ALLOYS 01f Georges Pirlot, Uccle-Brussels, Belgium, assignor to 'Solvay & Cie, Brussels, Belgium, a Belgian company No Drawing. Filed June 8, 1954, Ser. No. 435,347 Claims priority, application Belgium June 11, 1953 "'1 Claim. (Cl. 75-167) nv onre ates to a n wmetho o p o in 1 Y d and metals, p r icul ly he all y "W n h p qducti n ofrorganic lea p nd p cially tetraethyl lead.

Monosodium lead alloys corresponding to the formula bNa and ntaining substantially-90% 'i leaidi and of sodium by weight, are at the present time prepared by mixing the two metals in the fused state. The sodium used in these alloys is almost always obtained by electrolysis of a sodium salt in the dry-way.

Various methods have been proposed for separating the alkali metals from the dilute amalgams obtained by electrolysis of aqueous solutions of alkali metal salts in mercury cathode cells.

However, these processes all present difficulties due to the great afiinity of the alkali metals for mercury, which renders separation difficult.

The present invention has as object a process permitting the obtaining of alloys of lead and alkali metals from alkali metal amalgams and in particular from electrolytic amalgam, without separation of the alkali metal in the isolated state.

It is based on the property possessed by lead of modifying, in a manner favourable to distillation, the partial pressures of mercury and of alkali metal of binary mercury-alkali metal alloys.

According to the invention, the process of preparation of alloys of lead and an alkali metal from electrolytic amalgams obtained in mercury cathode cells consists in dissolving lead in the amalgam and eliminating the mercury of the ternary alloy by distillation.

The invention is applicable to the production of alloys of lead with one or more alkali metals, but in order to facilitate the understanding of the process, the invention will be described hereinbelow in its application to the production of lead-sodium alloys.

The dissolution of the lead in the amalgam is advantageously effected in the heat. When the dissolution is completed, the ternary amalgam is distilled in order to eliminate the mercury, which is condensed, collected, and returned to the electrolytic cells. A lead-sodium alloy containing only traces of mercury is obtained as distillation residue.

The mercury distilled off and recycled to the electrolytic cells should contain only small amounts of sodium. For this reason the atomic ratio Na/Pb in the alloy preferably lies within the range 0.1 to 3. The alloy which is particularly suitable for the production of tetraethyl lead may be prepared directly at the desired concentration. It is also possible to prepare an alloy having a greater or smaller concentration of sodium, the composition of which can subsequently be modified by dissolving a further quantity of lead or of metallic sodium therein.

The lead need not necessarily be introduced into the dilute electrolytic amalgam. It is sometimes advantageous to eliminate a part of the mercury from the dilute amalgam in order to increase the sodium content of the amalgam, and then to add the lead. The lead may be added in one or more times, the advantages resulting from the introduction of the lead being the greater, the higher the sodium content of the amalgam subjected to distillation.

2,990,276 E tat s! Ju e 27-. sea

earran e di illa aii at the m rcur mama he rna vf m s te rarlaq l ni m lgam, can-b2 im in a how distillation apparatus in which theamalgam flows over a metal Wall, through which is efiected the trans a the ea suit d-tor evaporation q rt i on rn r w a the. adv nt e Qt: Perm t: ting distillation: of a thin layer, thus. avoiding bumping dueto distillatiom; V l

"lhe-distillaf n may alsobe carried out continu usly in one or more fstages inv stillswhich. may or may not surmounted by extraction columns.

..'.Dist il1 tion several stages offers the advantagethat ar P t ith e ry' se m t at frr ssure close to atmospheric pressures. It also permits a de r e f cav ta i n Qt erc r f m fin l-le st sodium alloy.

The advantages of the invention are illustrated by the examples given below, which are in no way limitative.

Example 1 In dilute amalgam, containing 0.5% of sodium by weight and issuing from mercury cathode electrolytic cells, lead is dissolved so as to form a ternary alloy in which the ratio of sodium and lead concentration is equal to 0.5 at. Na/ at. P-b.

This amalgam is introduced continuously into a still operating at a temperature of 550 C. at an absolute pressure of mam/Hg. The vapours emitted are condensed by cooling and the condensate, composed of mercury containing only 1.0 at. percent of sodium, is recycled to the electrolytic cells.

A binary lead-sodium alloy corresponding approximately to the formula Pb lNa and containing only 2 at. percent of mercury is continuously collected from the still.

Example 2 To a dilute amalgam containing 0.5% by Weight of sodium issuing from electrolytic cells, lead is added so as to form a ternary amalgam of a composition such that the ratio of the sodium and lead concentrations will be equal to 1 at. Na/at. Pb.

This ternary alloy is introduced into the top of a trickle distillation apparatus and uniformly distributed over the internal face of the externally heated apparatus. This apparatus works at the normal pressure of 760 mm./Hg, while the temperature varies between 370 and 550 C. from the top to the bottom.

The vapours emitted are condensed and the condensate composed of practically pure mercury is recycled to the electrolytic cells.

The liquid ternary alloy leaving this distillation apparatus has the following composition:

This alloy is continuously introduced into the boiler of a still functioning at 550 C. at an absolute pressure of 10 rum/Hg. The dilute amalgam obtained by condensation of the vapours leaving said still has a sodium concentration of 5 at. percent. This amalgam is mixed with amalgam leaving the electrolytic cells for treatment in the trickle still after adding lead. The liquid alloy collected from the bottom of the boiler-still corresponds to the formula PbNa and its mercury content is only 2 at. percent.

It is obvious that numerous modifications exist in the carrying out of the process forming the subject of the invention. In particular, trickle stills may be replaced by boiler stills, and vice versa. Moreover, in multi-stage distillation processes an almost pure mercury fraction a subsequent stage. This operation enables the sodium ncentration of the vapours leaving theflast stage to be and't-liusavoids-fractional condensations obstructions which may resultfromth formation of "fiA'r'nethod of preparingdir'ectly an alloy oflead and of-an'alkali'metal 'froman amalgam previously produced b'y-ele'c'trolysis 1 in' a mercury cathode cell without prior recovery of the alkali metal from said'amalgam, "which Eon'rp'ri'se's dissolving lead 5 in said previously-pmduced amal am to form a ternary' amalgam in whichthe atomic ratio of sodium to lead concentrationis equalito' 111,111 troducing said ternary amalgam into a trickle' distillation lzonej operat'ing at atmospheric pressure and at atemr 'pera ture varying from 370-550" C. fi'onf'top to bottom condensing the vapors emitted from said distillation zone,

obtained hy condensation of the vapours first stage-may 'be utilised to condense" vapours produced in 10 References Cited in the fiIetOf this patentZe T H mg the condensate to said electrolytic cell, intro- "dncing the-residue fromssaid distillation zone into'a sec- 5 vapors leaving said second zone, mixing said condensate wit s i ma a n 'hb s 'e l trql fig-sd and collecting said alloy from the bottom of said second zone a 11".;

UNITED STATES PATENTS 269,853 Ewell Sept. 13, 1910 1 x245 Duhme ..a;. Nov;f1'6, 1925 5 1,-72s,ss9 Ormont Sept. 1'-7,f1929 2,082,362 Stevens f June-i 1 1937 FOREIGN PATENTS 714,456 Germany Nov. 2 9, 11941' 

